The use of both a "woofer", or bass notes only transducer, and a "tweeter", or treble notes only transducer, have constituted high-fidelity wide-range loudspeaker structures for some time. Time acoustic performance of the system, as judged at the listener's ears, determines the pragmatic results. The better this performance, the more nearly a life-like effect of "live" performers is obtained; i.e., "realism".
Sound Span Speaker Systems, of former B.I.C./AVNET, Westbury, N,Y., employ three transducers; a woofer pointing ("firing") downward, a mid-range transducer employing a horn, and a treble transducer also employing a horn. These transducers are positioned coaxially one above the other in the order recited; the latter two transducers firing upward.
By factual analysis, an omnidirectional sound pattern is presumably obtained, but it is not seen how this pattern could be obtained vertically as well.
The sound-emitting elements being stacked coaxially vertically, an away-from-the-wall placement of the loudspeaker would be required to give the intended omni-directional lateral sound fidelity. However, if placed against a wall the backwardly-directed sound conflicts with the direct sound, and an irregular amplitude vs. frequency characteristic occurs.
Williams, Jr. in U.S. Pat. No. 4,200,170, discloses a "Pyramid Speaker Assembly", having two vertically aligned four-sided pyramids and one cone loudspeaker firing downwardly upon the lower pyramid
An alternate embodiment merely doubles the structure vertically and employs two identical cone loudspeakers.
A further alternate embodiment assembles two of the initial structures, with one of them inverted, so that two cone loudspeakers are employed, one up-firing and one down-firing.
The four-sided pyramid causes a four-leaf clover horizontal dispersion of sound. The vertical pattern of the loudspeaker is not enhanced.
Typically, tweeters are not employed at all, save for a further embodiment in which a tweeter is disposed off-axis but "-in alignment with a ridge-" of pyramid. This causes a two-only (opposed) cloverleaf for the high frequencies involved.
It is seen that a uniform omnidirectional pattern for either woofer or tweeter sound is not attained.
The numerous sharp edges in the sound field are expected to give an uneven amplitude vs. frequency characteristic because of acoustic diffraction.
Westlund in U.S. Pat. No. 3,819,006, discloses a three-globe (sphere) structure, each having an identical loudspeaker within a globe, plus a spaced concave reflector that is elongated to serve the plural globes.
The acoustic structure and functioning thereof is quite the opposite of the present invention and cannot suggest the same. Standing waves occur within the globes.
Evans, in U.S. Pat. No. 2,065,367, discloses one loudspeaker adjacent to either a sphere or a second rigid cone; but this is only half of the Wolcott structure and cannot function like it. Evans experiences severe resonant distortion at audio frequencies where the average distance between the sphere and the cone of the loudspeaker is a half-wavelength of the sound.
Feller, in offenlegungsscrift 2701080, discloses two wide-frequency-range loudspeakers facing each other at adjacent apexes of truncated cones. There is no sound reflecting sphere, as in the Wolcott structure. There will be standing waves and consequent distortion in the frequency range where the average distance between the two loudspeakers is equal to a half-wavelength of the sound.
The problems in Evans and Feller are avoided in the Wolcott embodiments because the input signal frequency range is split with a crossover network between the woofer and tweeter and so proportioned that principal resonance conditions due to the spacing between the speakers and/or the sphere occur outside their primary operating frequency range.
Petroff, in Belgium Pat. No. 497,101, discloses two loudspeaker-microphone devices for communication through a wall; as from the exterior to the interior of a building. Frequency response does not appear to be involved, nor proximity effects between active audio elements.
In general, the art has been wont to combine plural loudspeakers, up to six per unit of a stero pair of loudspeakers, typically by merely firing the sound outward from the cabinet that supports the loudspeakers, but does not shape the sound pattern thereof.
Still others partially or totally enclose loudspeaker units in an enclosure that "colors" the sound by having a predominant resonant frequency. That causes the sound to have characteristic of particular musical instrument rather than a uniform amplitude vs. frequency that is suited to reproduce all musical instruments and voice with fidelity.